The NTSB has been advocating for inward and outward facing recorders for investigation and oversight purposes since 2007 and has previously made recommendations to the Federal Railroad Administration and other railroads regarding the matter.

The safety recommendations were developed from information learned during the ongoing investigation into the December 1, 2013, derailment of a Metro-North passenger train in Bronx, N.Y.

"The images and audio captured by recorders can be invaluable to our investigators," said NTSB Chairman Deborah Hersman. "Understanding what is happening inside the cab just prior to a crash can provide crucial information about how to prevent future accidents."

NTSB investigators say that they have learned that while Metro-North had posted signs for temporary speed restrictions throughout its rail property, it did not use signage for permanent speed restriction areas including the area where the accident occurred. Metro-North has since installed signage to aid operating crews at four locations with permanent speed restrictions, including the derailment area. However, the NTSB recommends a more systematic approach and says Metro-North should install signage at all locations where permanent speed restrictions are in place.